This invention relates generally to centrifugal compressors and, more particularly, to a method and apparatus for providing a relatively large diameter labyrinth seal between a transmission chamber and a low pressure area in a balance piston adjacent the impeller.
In order to counteract the aerodynamic thrust that is developed by the impeller of a centrifugal compressor, it is well known to employ a balance piston consisting of a low pressure cavity behind the impeller wheel. Because of the tendency for lubricating oil to leak from the transmission into this low pressure area, it is also common practice to install a labyrinth seal between the balance piston and the transmission. U.S. Pat. No. 4,997,340, assigned to the assignee of the present invention, describes such a labyrinth seal and a particular manner in which the seal is pressurized in order to obtain optimal performance in an economical manner. The full text of that patent is hereby incorporated, by reference, into this application.
The passage that is formed in the labyrinth seal of U.S. Pat. No. 4,997,340 is formed by first drilling a radially extending passage from the outer surface to the radially inner surface of the labyrinth seal, and then drilling another passage from the rear face of the seal to interconnect the radially extending passage. This method has been found satisfactory for relatively small and medium sized labyrinth seals.
The need has now arisen to install a larger diameter (i.e. in the range of 11 to 12 inch diameter) labyrinth seal in a centrifugal compressor. The normal method as described hereinabove can therefore not be used because conventional drilling techniques do not permit the hole to be positioned accurately enough to consistently intersect with the labyrinth teeth at the desired location. That is, because of the necessarily small thickness of the seal, the passageway must be of a small diameter. When using a small diameter drill bit, it tends to bend and wander from the intended path unless the length is kept relatively short.
It is therefore an object of the present invention to provide an improved labyrinth seal arrangement for a centrifugal compressor.
Another object of the present invention is the provision in a centrifugal compressor for a relatively large diameter labyrinth seal.
Yet another object of the present invention is the provision in a centrifugal compressor for effectively and economically forming the radially extending passage in a relatively large diameter labyrinth seal.
These objects and other features and advantages become more readily apparent upon reference to the following description when taken in conjunction with the appended drawings.